President Trump in the Oval Office at the White House on June 20. (Jonathan Ernst/Reuters)

The first major poll of opinions shows that the health-care bill under consideration in the Senate is about as unpopular as the one that passed the House. A PBS NewsHour-Marist poll released Wednesday reveals that only 17 percent of the country supports the Senate measure, known as the Better Care Reconciliation Act. Bad news for the Republicans advocating its passage, clearly.

Buried in the poll, though, is even worse news for the party. Democrats continue to be stalwartly opposed to President Trump and his party’s health-care proposals, unsurprisingly. But independents are similarly souring on the president and the party’s legislation — as Republicans and Trump supporters appear to tune out. November 2018 is still a long way away, but if that trend continues, it suggests the possibility of a disinterested Republican base and a hostile middle — bad news for Republicans in Congress in any sort of contested race.

Since February, approval of Trump’s job performance among independents has fallen by 9 points, from 40 percent to only 31 percent. Four months ago, Trump was 11 points underwater on favorability with that group, meaning that his unfavorable numbers were 11 points higher than his favorable numbers. That spread is now 28 points.

Part of this is Trump’s handling of the economy, with 49 percent of that group saying that the economy has weakened under his leadership. But part of the problem lies elsewhere.

Consider Obamacare. The Republican effort to repeal Barack Obama’s signature legislation has served only to make the bill more popular, with most Americans hoping it remains in place and a plurality thinking that it should be strengthened, not repealed.

If you consider those numbers by party, it’s striking how similar the independent numbers are to those among Democrats. Independents are slightly more likely to want to repeal Obamacare than are Democrats, but overall the group supports keeping and strengthening the legislation — not what Republicans in Congress are aiming to do.

Unsurprisingly, independents are generally hostile to the Senate legislation, with poll numbers that again largely mirror Democratic attitudes on the subject.

In that graph, though, notice the gray bars. More Republicans say they haven’t heard enough about the Senate bill than say they support it — a remarkable bit of data. Even among Trump supporters, the two figures are about equal — and only slightly higher than the percentage of Trump supporters who say they oppose the Senate measure.

Earlier this month, The Post’s Jenna Johnson reported that Trump backers who once hung on the president’s every word are starting to pay less attention, in part because so much of the news about his presidency has been negative.

Trump encourages his base to ignore the mainstream news media and, instead, champions his Twitter feed as a source of unvarnished updates about his policies. (Critics would point out that this is an inaccurate description of his often fact-free social media presence.) But nearly 4 in 10 Trump supporters say that his tweets are “reckless and distracting,” according to the poll, while fewer than half find it “effective and informative.” Overall, nearly 70 percent of Americans fall into the former category. If Trump wants to use his Twitter account to step around the media, it doesn’t seem to be working.

Only a third of American adults think that Trump is proving to be a more effective leader than Obama was, the poll found. By a more than 2-to-1 margin, independents held the opposite view. Even 1 in 10 Trump supporters believed Obama to be more effective, twice the percentage of Democrats who thought Trump was more effective than Obama.

Trump’s presidency has been predicated on making direct appeals to his base of support. On health care, there’s no group that supports what he and his party are doing more than those voters. But Trump won the presidency by the skin of his teeth, thanks in part to independents willing to give him a shot over Hillary Clinton. If those independents are as antagonistic to him and the Republicans by this point next year — and if Republicans continue to find it frustrating to hear about what Trump is doing both from the media and from Trump himself — it’s hard to think that the composition of Congress in 2019 will be as favorable to Trump’s party.